A conventional system that remotely controls an in-vehicle device conducts a bidirectional communication between the vehicle-side device and a mobile device such as an electronic key device to determine whether the mobile device is a regular or authorized mobile device carried by a user, as disclosed in, for example, JP 2000-104429A. This remote control system is a smart key system, and has a transmitter as the vehicle-side device so as to conduct the bidirectional communication between the transmitter and the mobile device.
A transmission request signal is transmitted to a given detection area from the transmitter. When the mobile device exists within the detection area to which the transmission request signal has been transmitted, the transmission request signal is received by the mobile device. The mobile device responsively transmits a given response signal in response to the transmission request signal. The response signal is received by a receiver equipped in the vehicle, and a given matching process is conducted on the response signal by a vehicle-side device. When the matching is confirmed, it is determined that the mobile device that has transmitted the response signal is an authorized mobile device. As a result, doors are unlocked, or an engine start is permitted based on the determination result.
In many instances, a plurality of mobile devices are provided to the owner of the vehicle so that not only the owner but also other persons such as the owner's family members may use the vehicle. Even if the mobile devices are different from each other, the control to be executed is identical if the mobile devices are the authorized devices. This is advantageous in that it is unnecessary for the user to be aware of which one of the mobile devices the user carries.
When a child is made to first get on the vehicle, it may be necessary to give the child the mobile device. However, when only the child having the mobile device exists within the vehicle, the child may erroneously starts the engine, and the vehicle moves in a state where only the child is in the vehicle. In order to prevent this situation, it is necessary to give the child no mobile device. However, this may cause some inconveniences in allowing the child first to get on the vehicle.